The present invention relates to a detector circuit and, more particularly, to a detector circuit for detecting the loss or reduction in dc power supplied to a dc load and for detecting a low battery voltage condition of a standby battery employed to power the load upon loss or reduction of dc power supplied to the load.
There are many applications in which it is desired to supply a dc voltage to a dc load while also having available a standby dc storage source, such as an electrical storage battery, which may be connected to the load in the event the voltage supplied to the load is terminated or reduced in value for some reason, for example, due to a loss of ac line voltage or failure of components used to derive dc voltages from the ac line voltage. In order to effect the transfer of the battery voltage to the load, it is generally necessary to provide some means, for example, in the form of detection circuitry, which detects the loss or failure of ac line voltage or of the dc voltage supplied to the load and thereupon automatically connects the battery to the load for utilization by the load in place of the original dc source. It may be further desirable following such a transfer operation, and especially after the battery has been in service for an extended period of time, to monitor the voltage of the battery and when the voltage of the battery has declined to a predetermined critical value to disconnect the battery from the load. This latter operation may be necessary to prevent permanent damage to the battery and also in those cases in which the dc load includes apparatus, such as microprocessor apparatus (e.g., of the MOS type), which has critical operating voltages below which the apparatus cannot function in the desired, efficient, error-free fashion.
The present invention is directed to simple, lowcost detection circuitry capable of satisfying the above mentioned considerations and requirements.